The present invention relates to a one-way clutch unit including a one-way clutch having rollers serving as engaging members and a ball bearing axially adjacent to the one-way clutch.
In a conventional one-way clutch unit of this kind, a one-way clutch and a deep groove ball bearing separate from the one-way clutch are axially adjacently disposed, so that the deep groove ball bearing receives a load to secure engagement performance of the one-way clutch and its durability.
However, the conventional one-way clutch unit needs a large number of component parts owing to the provision of the separate deep groove ball bearing and has an increased axial dimension accordingly. Thus the one-way clutch unit is necessarily high in cost and large in size.
Therefore, it is an object of the present invention to provide a one-way clutch unit that allows reduction of the manufacturing cost and size by reducing the number of component parts thereof and its axial dimension.
In order to accomplish the above object, a one-way clutch unit according to the present invention comprises:
a one-way clutch having rollers serving as engaging members and a retainer for retaining the rollers; and
a ball bearing disposed axially adjacent to the one-way clutch and having balls and a retainer for retaining the balls, wherein:
the one-way clutch unit comprises:
a one-piece outer ring having a first outer ring part for the one-way clutch and a second outer ring part for the ball bearing, both parts being integral with each other; and
a one-piece inner ring having a first inner ring part for the one-way clutch and a second inner ring part for the ball bearing, both parts being integral with each other.
In the one-way clutch unit, the first outer ring part for the one-way clutch is integral with the second outer ring part for the deep groove ball bearing to compose the one-piece outer ring, and the first inner ring part for the one-way clutch is integral with the second inner ring part for the deep groove ball bearing to compose the one-piece inner ring. Thus the number of component parts of the one-way clutch unit is reduced as compared with the aforementioned conventional unit. Also, it is possible to reduce an axial length of the one-way clutch unit. Therefore it is possible to reduce the cost and the size.
In one embodiment, the first outer ring part has a cylindrical inner peripheral surface, and the first inner ring part has a polygonal outer peripheral cam surface. The retainer for the ball bearing is a snap cage having an annular portion. The one-piece inner ring has a tapered surface between the polygonal outer peripheral cam surface of the first inner ring part and an outer peripheral surface of the second inner ring part, and the annular portion of the snap cage is disposed between the tapered surface of the one-piece inner ring and an inner peripheral surface of the one-piece outer ring opposed to the tapered surface.
This embodiment effectively utilizes a space between the tapered surface (present between the polygonal outer peripheral cam surface of the first inner ring part and the peripheral surface of the second inner ring part) of the one-piece inner ring and the opposite inner peripheral surface of the one-piece outer ring to dispose the annular portion of the snap cage. Thus, it is possible to prevent an increase of an axial dimension due to the provision of the snap cage.
Further since the annular portion of the snap cage is disposed on the clutch side, a space on the side opposite from the clutch increases. Therefore it is possible to facilitate or enhance circulation of grease and hence reduce the pressure of the grease. As a result, compared with a case where the annular portion is disposed not on the clutch side, but on the counter-clutch side, i.e., side opposite from the clutch, it is possible to prevent leak of the grease to a higher extent.
The tapered surface can be obtained by cold-forging the polygonal outer peripheral cam surface of the first inner ring part of the one-piece inner ring.
The retainer for the one-way clutch may have a stepped portion serving as a grease reservoir at an annular portion thereof opposite from the ball bearing.
This arrangement allows grease to be easily stored, which contributes to reduction of the pressure of the grease and prevents leak of the grease. Further it is possible to increase a grease-storing capacity and improve the life of the grease.
The one-piece outer ring may have an annular groove serving as a grease reservoir at an inner peripheral surface thereof.
This arrangement increases the grease-storing capacity. Thus an increased volume of grease can be loaded and the life of the grease can be improved.
The one-piece inner ring may have an axial length longer than that of the one-piece outer ring and a clutch-side end of the one-piece inner ring may project axially beyond a clutch-side end of the one-piece outer ring.
In a case where a rotational shaft inserted in the one-piece inner ring has a flange extending radially outwardly along the clutch-side end of the one-piece inner ring and then along the clutch-side end of the one-piece outer ring beyond the one-piece outer ring, the clutch-side end of the one-piece inner ring projecting axially beyond a clutch-side end of the one-piece outer ring prevents the flange of the rotational shaft from interfering with the axial end surface of the one-piece outer ring. Thus the assembling performance can be improved.
In one embodiment, the first inner ring part of the one-piece inner ring has an annular groove at an outer peripheral surface thereof at a side opposite from the bearing. On the other hand, the retainer for the one-way clutch has a counter-bearing-side annular portion, and the annular portion has a projection projecting radially inward. The projection is fit in the annular groove so that the retainer for the one-way clutch is axially locked to the first inner ring part.
This arrangement eliminates use of separate component parts for locking the retainer such as a snap ring. Thus it is possible to reduce the number of component parts, improve the assembling performance, and reduce the axial dimension.
In one embodiment, the first outer ring part has a cylindrical inner peripheral surface, and the first inner ring part has a polygonal outer peripheral cam surface, and the retainer for the one-way clutch has a polygonal inner peripheral surface portion that engages with the polygonal outer peripheral cam surface of the first inner ring part.
In this embodiment, fitting the polygonal inner peripheral surface portion of the retainer onto the polygonal outer peripheral cam surface of the first inner ring part achieves a function of locking the retainer against rotation. Therefore it is unnecessary to use additional component parts for that purpose and the size reduction is achievable.
The retainer for the one-way clutch may have a bearing-side annular portion and a bearing-side axial end of an inner peripheral surface of this annular portion forms a tapered surface that widens as moving axially outwardly.
The tapered surface at the axial end of the bearing-side annular portion of the retainer for the one-way clutch, which widens as it goes axially outwardly, serves as a guide surface for an outer peripheral surface (e.g. a polygonal cam surface) of the first inner ring part of the one-piece inner ring in assembling the unit. Thus the retainer can be easily mounted around the one-piece inner ring.
When the second outer ring part and second inner ring part for the ball bearing each have a raceway surface whose radius of curvature is in a range of from 50.5% to 51.5% of a diameter of the balls, the inclination of the one-piece outer ring with respect to a rotational axis decreases. As a result, the engagement performance in the one-way clutch and its durability can be improved. If the radius of curvature is less than 50.5%, the balls are so tightly engaged with the raceway surfaces that a smooth rotation of the balls is inhibited. On the other hand, if the radius of curvature is more than 51.5%, the effect of reducing the inclination of the one-piece outer ring deteriorates.
When each roller of the one-way clutch has an axial length in a range of from one to two times as large as a diameter of the roller, it is possible to restrain or minimize a difference in the distance from the outer peripheral surface of the first inner ring part to the inner peripheral surface of the first outer ring part between at both axial ends of the rollers, which would occur when the one-piece outer ring is inclined. Thus the engagement performance in the one-way clutch and its durability can be improved. If the axial length of the rollers is less than the diameter thereof, the frictional torque of the rollers becomes insufficient. On the other hand, if the axial length of the rollers is more than twice as large as the diameter thereof, the effect of restraining the above difference deteriorates.
Also, if a radial gap of the ball bearing is set to a value in a range of 0 xcexcm to 20 xcexcm when the one-piece outer ring is press-fitted into a housing, the inclination of the one-piece outer ring with respect to the rotational axis of the one-piece inner ring is suppressed, and the engagement performance in the one-way clutch and its durability can be improved.
In one embodiment, the one-way clutch and the ball bearing are lubricated with same grease, and one-way clutch unit has a sealing device disposed at both axial ends thereof between the one-piece outer ring and the one-piece inner ring. This arrangement simplifies the lubricating and sealing structures, which facilitates the size reduction of the one-way clutch unit.